Vivitar 283 Manual Power Controller

I've recently become addicted to the
Strobist movement started by
David Hobby, which teaches camera lighting techniques using off-camera
Speedlights. Strobists typically set their flash power manually rather
than relying on TTL or other new-fangled systems that require sophisticated
means of communication between the camera body and flashes.

I'm also very found of finding old, inexpensive, yet high quality
equipment and using it along with my digital body. Most often, this
means lenses, but I've also picked up a couple older flashes and some
other equipment.

Trigger Voltage

The one thing to keep in mind when using older flashes on digital bodies
is the trigger voltage used by the flash. This is the voltage across the
terminals which, when shorted, will cause the flash to fire. This could
mean the terminals on the PC-sync port or the bottom & top of the hot shoe.
Older, manual bodies didn't care much what the voltage, so flash
manufacturers didn't, either. Consequently, trigger voltages could be
anywhere between 4V and 400V. Modern digital cameras are much more
picky, and can be severely damaged by anything more than about 6V (Canon)
or 12V (Nikon). The most comprehensive list of strobe trigger voltages
I've found is here.

There are a couple ways to get around this. The route I chose is to get
a model of wireless flash trigger (the
Cactus V4)
that is designed to handle a trigger voltage of up to 300V.
You could alternatively get a
Wein Safe Sync,
a small hot shoe adapter which will convert the flash's trigger voltage
down to 6V for the camera body. They're a little pricy at $50, and you
need one for each flash.
Or, you could limit your choice of flashes to those with safe trigger
voltages.

In addition to my modern
Canon 430EX,
I also own a
Sunpak 544
"potato masher" flash, which triggers at 6.7V,
and the venerable
Vivitar 283,
which fires at a variety of voltages
depending on when and where the flash was made. Japanese models can
trigger at 300V. Korean models trigger as low as 6V. My Chinese model
triggers at 9.4V. 9.4V would work for Nikon, but is a little hot for
Canon. Good thing my Cactus V4's don't care.

Manual Power Control

Most older flashes were designed to automatically fire at the correct
power based on a sensor on the front of the flash. Some flashes,
like my Sunpak 544 or the Vivitar 285, also had a dial that
allowed the user to manually set the power of the flash. This sort
of manual control is necessary for use by Strobists. Alas, the
Vivitar 283 (the 285's little brother) has only a full power
manual setting, with no capacity to lower it. The 283 is a cheap
($20-30), plentiful (manufactured from 1972-2007), durable, workhorse
of a flash, though, which makes this sort of problem worth working around.

Vivitar used to market the "VP-1," a device which replaced the thyristor
and provided a dial for continuously variable power control down to
1/32 power. However, Vivitar discontinued the VP-1 along with the 283
around 2007, and they're rather rare and expensive on eBay.

According to
Charles Krebs,
The 283's power can be reduced by placing a variable amount of resistance
between two terminals on its front plug. I've seen a few different
methods for implementing this, including
this one by Eric Au and
the Vivitar Lancer by Lance Earl.
However, most of these options eliminate the auto power feature, and
many of them even eliminate full power mode due to the type of pot
(variable resister) used. I didn't like either of these problems, so
I chose to follow a slightly different design.

I did this by removing the auto thyristor sensor from its plug on the
front of the flash. I unscrewed the plug from the rear of the thyristor
and attached it (through a 1/8" spacer) to the back of a 3x2x1" plastic
project box. The main body of the thyristor is screwed to the front of
the project box.

Also on the front of the box, right next to the thyristor, is a 100k-ohm
potentiometer. According to Krebs' site, the 283 reaches full power when
the two terminals at the right of the thyristor plug (when staring at
the front of the flash) are connected with 150k-ohm or more resistance.
The flash is reduced to 1/2 power at about 78k-ohm, which is why I chose
to use a 100k-ohm resistor. The resolution provided by the 100k-ohm pot
allows me to dial the flash down to about 1/128 power (7 stops) with
some degree of accuracy, although the settings get pretty close together
beginning with the 4th stop.

The third item on the front of the project box is a DPDT switch that
allows me to choose between the auto/full power (factory) setting and
the reduced power controlled by my new dial. The thyristor and the pot
are wired to the two sides of the switch, and the center of the switch
is wired to the original thyristor plug on the back of the box.

The advantage of my setup over others is that, while adding manual control
down to 1/128 power, I've still retained the original factory configuration
with its automatic power settings. In addition, this mod is completely
reversible with a little bit of soldering, in case I want to return the
flash to its factory trim at a later date.

I'm reasonably happy with this setup. The box doesn't fit quiet as
tight onto the flash body as I'd like due to a slightly thinner spacer
between the box and the plug, but it's usable. I could have used a
somewhat smaller (especially thinner) box, but this is the smallest
that RadioShack had available. The resulting box is a little bulky.

Would I do this mod again? I'm not sure. It works well and didn't
cost much, but it was far more time consuming that I expected, and it
makes for a rather bulky appendage to the front of the flash. Most
of the time was spent in the design phase; I could make a second one
rather quickly now. Still, I think I'd prefer to find a different
model of flash that already had manual control from the factory.

Photos follow. I'll let you figure out which shots represent which
step in the process.

Project Photos and Test Shots

The following shots were taken in manual power mode. Yes, they're
out of focus. I was only testing the exposure. These were taken in
a dark (but not black) room at ISO 100, 1/125s, f/8. The flash was
at 45 degrees to camera left, about 18" from the subject. The last shot
(7 stops below full) appears to be more than 1 stop below the 1/64
shot, but that's because the marks on the dial are very close together
in that range, and it's hard to set it just right. There was no
noticeable difference in flash power below 1/128.

The following shots were taken using the automatic power settings in
the factory configuration. The theory is that you set your ISO speed
on the calculator dial (by the bounce hinge), then pick which of the
four settings (designated by different colored indicators on the thyristor)
matches your current distance and camera settings. The sensor on the
flash will then throw out what it senses as the proper amount of light for
your scene. The range for each color is: Yellow: 5-43', Orange: 4-30',
Blue: 2-15', Purple: 2-11'.